1. Field of the Invention
This invention relates to a photovoltaic device and a manufacturing method of the photovoltaic device.
2. Description of Prior Art
Photovoltaic devices are broadly categorized into single crystalline-, polycrystalline-, and amorphous-based type depending on a type of a semiconductor of a part for converting absorbed light into electric current. By taking advantage of features of the amorphous semiconductor thin film and crystalline semiconductor, a hybrid photovoltaic device with both types of semiconductor laminated has been researched. For example, U.S. Pat. No. 5,213,628 discloses a photovoltaic device of this kind. In this photovoltaic device, a substantially intrinsic amorphous silicon thin film is placed at a junction interface in forming semiconductor junction by combining a crystalline silicon semiconductor and an amorphous silicon semiconductor having different conductivity from each other so as to improve interface characteristics and photovoltaic conversion characteristics.
FIG. 5 is a perspective view of a photovoltaic device having a structure of which a substantially intrinsic (i-type) amorphous semiconductor layer is placed at a junction interface between an amorphous semiconductor and a single crystalline silicon semiconductor whose surface is textured. In this specification, the substantially intrinsic amorphous semiconductor includes both of an intrinsic amorphous semiconductor formed without the introduction of dopant and a substantially intrinsic amorphous semiconductor doped with a small number of atoms belonging to group 3B of the periodic table such as boron.
As shown in the FIG. 5, surfaces of an n-type single crystalline silicon (Si) substrate 101 are textured by alkaline etching or the like. An i-type amorphous silicon (a-Si) semiconductor layer 102, a p-type amorphous silicon (a-Si) semiconductor layer 103 and a transparent electrode 104 composed of a transparent conductive film such as an ITO (Indium Tin Oxide) film are laminated in this order on the textured surface on a light receiving side of the single crystalline silicon substrate 101. Additionally, comb-shaped collector electrodes 105 of silver (Ag) for example are formed on the transparent electrode 104.
An i-type amorphous silicon (a-Si) semiconductor layer 106, an n-type amorphous silicon (a-Si) semiconductor layer 107 and a transparent electrode 108 composed of a transparent conductive film such as an ITO film are laminated in this order on a rear surface of the single crystalline silicon substrate 101 to achieve BSF (Back Surface Field) effect. Additionally, comb-shaped collector electrodes 109 of silver (Ag) for example are formed on the transparent electrode 108.
With above structure, light reflection is suppressed by the textured surface so that light can be taken into the device effectively.
As can be appreciated, the characteristics of the interface between the single crystalline silicon substrate and the amorphous silicon thin film are improved by interposing the substantially intrinsic amorphous silicon thin film without dopant or with trace amounts of boron doped when the crystalline silicon substrate and the amorphous silicon thin film having different conductivity from each other are combined to form a p-n junction. The p-n junction of this structure can be formed at a temperature of not higher than 200° C. that is relatively low temperature in junction forming. Therefore, excellent junction characteristics can be obtained even with an impure substrate, which is subject to an adverse effect of impurity or deficiency of oxygen induction under a high temperature process.
The p-n junction formed at a temperature of 200° C. or lower has excellent junction characteristics. However, even the excellent junction characteristics has some room for improvement.